The present invention relates to a new and improved method of forging a metal workpiece in a press, and more particularly to a method of forging a metal workpiece having a hole which extends through the workpiece.
Workpieces having through-holes, such as gear blanks, have previously been forged in presses. In forging the workpieces, mandrels have been used to form and locate holes in the workpieces.
During warm and hot forging, a workpiece is chilled by the die due to temperature differences between the workpiece and the mandrel. As this chilling occurs, the workpiece shrinks, due to thermal contraction. This locks the workpiece onto the mandrel at the through-hole location. When the workpiece is stripped from the forging mandrel, relatively high ejection loads are encountered. For presses with weak ejection systems, the pressure needed to overcome the workpiece stripping load may exceed the capacity of the press.